1. Technical Field
This disclosure relates to multiple input multiple output wireless communication systems that include base stations and user equipment. More particularly, this disclosure relates to a wireless communication system that includes a radio frequency assistant configured by user equipment to assist in radio frequency signal transmissions.
2. Description of the Related Art
Multiple input multiple output technology increases the strength, power, and reliability of wireless signal transmissions through the implementation of multiple antennas. The use of multiple input multiple output technology uses a plurality of antennas to enhance performance through increased data transmission and increased spatial diversity. In current spatial diversity systems, multiple antennas at a base station or multiple antennas at a terminal may operate at the same carrier frequency. For example, a plurality of antenna elements operating at a receiver may receive independent transmissions on the same carrier frequency and enhance performance by decreasing the amount of interference with a signal. Similarly, a plurality of antenna elements at a transmitter increases the capacity of the data transmission.
In current spatial diversity systems, the spacing between the antennas at a transmitter and the antennas at a receiver may have an impact on the correlation between the transmitter antennas and between the receiver antennas. The correlation between closely spaced antennas may reduce any multiple input multiple output spatial diversity and multiplexing gains. Generally, correlation decreases with an increase in antenna separation. Experimental results and measurements suggest that antennas may be decorrelated at a transmitter or a receiver by spacing apart antenna elements at about a physical distance of half-lambda, λ/2, where λ is the wavelength of a carrier radio wave or radio frequency signal. The experimental results and measurements also show that receiver antennas benefit from performance improvements up to a distance of approximately 3λ.
For example, at a frequency of 700 MHz, a physical distance of half-lambda, or approximately 21.4 cm, would be required for antenna decorrelation to achieve independent antenna operation. In a compact wireless device, such as a handset or similar wireless cellular system, this physical spacing between multiple antennas is challenging to achieve on a single device because of the limited amount of space available within such small devices.